In recent years, an increasing number of portable terminals such as cell phones or PHS (Personal Handyphone System) have a touch panel. There is a known portable terminal in which a touch panel is arranged on a display unit and at a part other than the display unit and a key part is arranged outside the display unit on the touch panel. An example thereof is illustrated in FIG. 9.
FIG. 9 illustrates a structure of a touch panel used for a portable terminal in a related art. A touch panel 1 illustrated in FIG. 9 is arranged on a display unit 2 and on a part other than the display unit 2 extended from the display unit 2. Touch keys 31 (three touch keys S1, S2, and S3 in the illustrated example) configuring a key part 3 are arranged outside the display unit 2 on the touch panel 1. With the structure, when a finger touches the touch panel 1, a coordinate corresponding to the touched position on the touch panel 1 is notified to a CPU (Central Processing unit) (not illustrated) at certain intervals, and a user's touch on the touch key S1, S2 or S3 is processed as key pressing.
In this case, when the user slides a finger toward the key part 3 from a position P11 on the display unit 2 on the touch panel 1 to a position P12, if the finger erroneously goes to the outside of the display unit 2 and erroneously touches a position P13 of the touch key S1 in the key part 3, the erroneous touch is processed as key pressing on the touch key S1, which causes an erroneous operation.
In order to prevent such an erroneous operation, there is considered that a distance (area B in the Figure) between the display unit 2 and the touch keys S1, S2, S3 is made longer, but this has a drawback that the device increases in size.
There is further considered that a touch is not processed as key pressing until the finger's touch on the touch key S1, S2 or S3 is detected for a certain period of time, and this obtains some advantageous effects but an erroneous operation is difficult to be eliminated.
There is further considered that when a finger is placed on the display unit 2 of the touch panel 1, the placement is not processed as key pressing until the finger is released or a certain period of time elapses from the release of the finger, but in this case, there is a drawback that if while the finger maintains placed on a position P31 on the display unit 2 in the Figure, for example, other finger touches the position P13 of the touch key S1 in the key part 3 or a position P23 of the couch key S3, the touch is not processed as key pressing.
There is further considered a method for detecting that a finger is slid from the display unit 2 toward the touch keys S1, S2 and S3 and controlling subsequent key pressing, but in this case, there is a drawback that a processing of detecting the finger sliding increases. With the method, for example, when the user slides a finger from a position P21 on the display unit 2 toward a position P22 to release from the touch key S3 side, if the finger erroneously touches the position p23 of the touch key S3 in the key part 3 before touching the position P21 on the display unit 2, an erroneous operation cannot be prevented.
As a prior art for preventing an erroneous operation of a touch panel in relation to the above, Patent Literature 1 describes therein an image display device for setting a prohibition area on a touch panel, if a finger erroneously touches the prohibition area for erroneous input, erasing the displays of icons, and displaying an alarm therefor. The device causes the user to recognize the situation, thereby to prevent an erroneous operation or the like.
Patent literature 2 describes therein an information processing apparatus comprising a touch panel on a display unit for counting a touch duration onto a predetermined region on the display unit, and controlling to perform a function assigned to a specific region when the touch duration from a touch state onto the specific region to a touch-up state does not reach a predetermined time, and not to perform the function assigned to the specific region when the touch duration reaches the predetermined time. Thereby, erroneous operations on the touch panel can be more accurately reduced without limiting a layout of the touch operation unit on the touch panel.